**7. Advantages and disadvantages of anaerobic digestion**

The advantages of anaerobic digestion are:


However, it has also certain disadvantages:


160 Biogas

There are many industrial applications in which the principal goal of anaerobic digestion is the organic treatment of waste instead of the production of gas. On this subject, the elimination of the difference between the organic matter contained before and after treatment, is a significant parameter that it is necessary to control. This is measured in term of Total solid (TS), volatile solid (VS), total organic carbon (TOC), COD or BOD (Boe & al., 2005). These parameters are

The carbon monoxide is a possible intermediate in the metabolic route of the acetogens and the methanogens (Moletta, 1993); Carbon monoxide was found in a great quantity during toxic inhibition by heavy metals (Liu & al., 2003). According to Moletta (Moletta, 2002) the presence of carbon monoxide is directly related to the acetate concentration, and conversely

**N.B**: there are other process control parameters of the production of biogas during anaerobic digestion, but they do not find any wide application in practice. However, the hydrogen gas is controlled in the gas phase and its measure in the liquid phase enables the identification of the existing different types of bacterial populations which may influence the process of

**6. Physicochemical conditions necessary to anaerobic digestion**  The anaerobic digestion can be carried out only under the following conditions:

• concentration in volatile fatty acid (VFA) lower than 2 – 3 g/l (McCarty, 2001).

• A production of a Biogas which may undergo beneficiation in the form of energy

• An agronomic interest, related to a significant phosphate and ammoniacal nitrogen concentration (NH4 + (PO4 3) due to the lysis of the organic matter (Münch & Greenfield,

• the possibility of treating high organic loads: from 2 to more than 80 kg of COD per

cubic meter of digester and per days, with a treatment rate from 80 to 98%

• a partial hydrogen pressure: 10 – 20 Pa to the maximum (Trably, 2002) • a potential of oxydoreduction lower than -300 mV (Suh & Roussaux, 2002)

• absence of oxygen, nitrates or sulphates (Degrémont, 2004). • pH close to neutrality: optimum 6,8 – 7,5 (Moletta, 2002)

• absence of inhibiting elements: agent chlorinated, antibiotic,… • an optimal stable temperature for micro-organisms (Bitton, 1994)

**7. Advantages and disadvantages of anaerobic digestion** 

• A reduction of the number of pathogenic micro-organisms;

• Request lower energy compared with aerobic processes ;

The advantages of anaerobic digestion are:

• A reduction of about 50% of the dry waste;

(heating, cogeneration of electricity);

1998);

appropriate for the control of the anaerobic digestion applied to several types of waste.

**5.5 Organic matter reduction** 

**5.6 Carbon monoxide** 

the anaerobic digestion.

related to that of methane (Batstone & al., 2002).

